An exhaust gas control apparatus for an internal combustion engine is known (refer to PTL 1) in which an engine intake passage and an engine exhaust passage are connected to each other by an exhaust gas recirculation passage, an exhaust gas recirculation control valve controlling an exhaust gas recirculation rate is disposed in the exhaust gas recirculation passage, a rich control for temporarily declining an air-fuel ratio of exhaust gas discharged from an engine combustion chamber is performed in a state where a throttle opening degree is decreased and the exhaust gas recirculation rate is reduced, and an opening degree of the exhaust gas recirculation control valve is decreased along with the decrease in the throttle opening degree, such that the exhaust gas recirculation rate is reduced, when the rich control is initiated.
In addition, another exhaust gas control apparatus for an internal combustion engine is also known in which the air-fuel ratio of the exhaust gas discharged from the engine combustion chamber is temporarily declined by an additional fuel being injected into a cylinder in an expansion stroke or an exhaust stroke in a state where the throttle opening degree is decreased and the exhaust gas recirculation rate is reduced during the rich control. In this exhaust gas control apparatus, the rich control is performed in the state where the throttle opening degree is decreased and the exhaust gas recirculation rate is reduced, and thus an additional fuel amount that is required for the air-fuel ratio of the exhaust gas to be enriched can be reduced.
Furthermore, an internal combustion engine is also known that is provided with an exhaust turbocharger which drives a compressor disposed in an engine intake passage on the upstream side of a throttle valve with an exhaust turbine disposed in an engine exhaust passage, a high pressure exhaust gas recirculation passage which connects the engine exhaust passage on the upstream side of the exhaust turbine and the engine intake passage on the downstream side of the throttle valve to each other, a low pressure exhaust gas recirculation passage which connects the engine exhaust passage on the downstream side of the exhaust turbine and the engine intake passage on the upstream side of the compressor to each other, a high pressure exhaust gas recirculation control valve which is disposed in the high pressure exhaust gas recirculation passage so as to control a high pressure exhaust gas recirculation rate, and a low pressure exhaust gas recirculation control valve which is disposed in the low pressure exhaust gas recirculation passage so as to control a low pressure exhaust gas recirculation rate.